This invention relates to a tool for the replacement of underground plastic pipe, such as water service lines and the like, whereas the existing pipe is split and expanded, while a replacement pipe is simultaneously pulled into said pipe.
Many underground plastic pipes, particularly those running from a water main into a residence, have degraded since original installation. As a result of this degradation, these pipes have begun to leak, and require replacement. Typically, a trench is excavated along the full length of the pipe, and a new pipe is installed in the trench, thereby bypassing the original pipe. The excavation can be a long and tedious process, damaging lawns and landscaping. It also risks the possibility of severing cables or other underground utilities.
A number of apparatuses have been developed for the replacement of underground pipe that is made from cast iron, steel, lead, and plastic. In the case of replacement of brittle or fracturable cast iron gas or water mains, a process of bursting the pipe can be used through the application of pressure to the interior walls, as illustrated by U.S. Pat. No. 4,505,302 (Streatfield et al) U.S. Pat. No. 4,732,222 (Schmidt) and U.S. Pat. No. 5,302,053 (Moriarty). Steel pipes can be split using a cutting wheel, then spread apart to allow a replacement pipe to be pulled into place, as illustrated by U.S Pat. No. 4,903,406 (Schosek et al) U.S. Pat. No. 5,306,101 (Rockower and Marazzo) and U.S. Pat. No. 5,439,320 (Abrams). Multiple radial blades are proposed in U.S. Pat. No. 5,076,731 (Luksch) and U.S. Pat. No. 5,544,977 (Cravy and McCall) for the splitting of buried steel and plastic pipe respectively.
While experimenting with previous prototypes, the applicant has found that pipe replacement tools with multiple blades greatly increase the amount of pulling force required, particularly while the tool is being pulled through a curved section of pipe. Opposing blades have a tendency to cause the tool to move off center within the pipe. As a result, the tool is forced against one side of the pipe, thereby increasing drag. Multiple cuts also allow greater amounts of grit and debri to accumulate between the split pipe and the replacement pipe. This debri further increases drag.
The apparatus described by U.S. Pat. No. 5,078,546 (Fisk et al) was specifically designed for replacing 4 inch buried steel pipe with plastic pipe. The apparatus includes a cutting wheel, forward of the cutting blade, to initially groove and weaken the pipe along the intended line of cut. In addition to a pulling cable, a pneumatically operated impact ram is described which attaches to the rearward end of the tool. Neither of these attributes are implied in the description of the tool herein proposed.
The apparatus in U.S. Pat. No. 6,092,553 (Hodgson) is also pulled through underground pipe by a cable. It has a single cutting edge for splitting the pipe, and a large cross section at the rear of the tool for the purpose of spreading the pipe, allowing a replacement pipe to be pulled into place simultaneously. Despite its apparent similarities to the proposed patent, the emphasis in U.S. Pat. No. 6,092,553 is placed on the cable used to pull the tool through the underground pipe. This emphasis stems largely from the fact that the particular application of this patent is the replacement of lead pipes carrying water from a main to a residence. The ability to initially thread a pulling cable into a lead pipe is of special concern because a larger cable is needed due to the much greater forces needed to cut lead pipe as compared to plastic pipe. Mineral deposits, which commonly adhere to the walls of older lead pipe, further inhibit ones ability to install a pulling cable.
As can be interpreted from FIG. 6 of U.S. Pat. No. 6,092,553, which is a plan view showing the typical location where the method of invention would be carried out, the intent of the invention is to replace relatively straight sections of buried pipe. This interpretation is reinforced by FIG. 1 which shows that the tool is relatively long and only very gradually tapered. As a result, the pulling of the tool around curved sections of pipe would be considerably inhibited. Because the type of plastic pipe used to bring water into a residence is commonly taken off a coiled reel, the pipe has a tendency to return to its original shape, thereby resulting in a gentle spiral. In addition, the plastic pipe may be intentionally bent to avoid obstructions, or direct it into a residence, or the settling of the surrounding soil may bend the pipe. Such curves in the buried pipe would significantly restrict the advancement of the tool through the under ground plastic pipe.
Another problem encountered in the development of the tool proposed herein was the susceptibility of the cutting blade becoming caught on objects surrounding the buried pipe such as roots or rocks. This problem is not as much of a concern when replacing lead or steel pipes because huge pulling forces and/or impact ramming is required to split the metal or cut through couplings. Such forces are sufficient enough to push aside extraneous obstacles surrounding the pipe. However, it does become a concern when only the greatly reduced forces are applied when replacing plastic pipe. Even a blade that only slightly protrudes through the wall of the plastic pipe can constrain the motion of the tool.
It is the object of the applicant""s invention to overcome the deficiencies of prior art devices used in the replacement of underground plastic pipe. In particular, the inability of prior art devices to negotiate bends in underground pipe, and their tendency to become caught on objects surrounding the buried pipe.
This invention is a tool that is pulled through an underground plastic pipe, simultaneously cutting it and pulling a replacement pipe into place. A typical application of the tool would be in the replacement of a water line located between a residence or business, and a shutoff valve at the water main. A stranded steel pulling cable is threaded through the buried pipe and then attached to the tool. A section of copper pipe is then attached to the rearward portion of the tool. A force is applied by the cable, thereby pulling it into the underground pipe.
As the tool advances, a cutting blade scores the inside of the pipe. Because the height of the blade is limited, it does not completely penetrate the wall of the plastic pipe, and therefore, the blade does not protrude from the pipe. Consequently, it is much less likely that the blade will become hung up on tree roots or rocks that may surround the buried pipe. The gradual increase in diameter towards the rear of the proposed tool creates pressure on the inside walls of the plastic pipe causing it to split at the point where it was scored by the blade. The splitting and spreading of the buried pipe allows room for the replacement pipe to be pulled into place behind the tool.
The tapered shape of the proposed tool allows it to be pulled around bends in the buried pipe. Any straight edges or excessive tool length, as exemplified in the drawings of U.S. Pat. Nos. 5,078,546 and 6,092,553 will cause these tools to become hung up within a bend on the outside wall of that bend.